Open Ended Questions – Advice
The most important message is to write as much correct information as you can that relates to the
question! Make sure you have answered the question!
Don’t be put off by the model answers – they were written by a teacher who has been studying
chemistry for a long time! Just do your best and try to write at least three points of correct
information!
If the question is about elements:
Try to mention correct information about
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atomic number and mass number
group in the periodic table, number of outer electrons
elements in the same group have the same chemical properties
as you go down a group the physical properties change
whether they are solid, liquid or gas
If the question involves molecules, compounds:
Try to mention information about
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bonding and properties (revise here
http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/periodic_table/metalsrev
4.shtml)
include conduction
solubility, melting and boiling points (from the data book)
If the question involves electricity:
Try to mention information about
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the electrochemical series (from the data book)
an explanation of oxidation (loss of electrons), reduction (gain of electrons)
how electrons flow from metals higher in the electrochemical series to lower in the
electrochemical series
any advantages or disadvantages about the environment (pollution, recycling, lack of
availability of metals from the Earth’s crust)
If the question involves homologous series:
Try to mention information about
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functional groups (carbon to carbon double bonds C=C, hydroxyl OH, carboxyl COOH)
formula – molecular, structural
increasing the number of carbons increase the boiling point and viscosity, decrease the
volatility
any advantages or disadvantages about the environment (pollution, recycling, use as fuels
etc)
If the question is about Fertilisers:
Try to mention information about
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N, P and K essential elements
Solubility
Pollution
Haber / Ostwald
Natural v Synthetic
If the question is about metals:
Try to mention information about
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Reactivity series
Whether it is found combined (reactive element) or uncombined (silver, gold)
Energy needed to extract the metal (cost)
Pollution – CO2 formed to produce that energy
Availability of metals is low as they are finite
Properties and uses
If the question involves acids and bases (alkalis are soluble bases):
Try to mention information about
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Neutralisation reactions
o Acid + alkali → Salt + water
o Acid + carbonate → salt + water + carbon dioxide
Write balanced equations
Names of salts
pH
H+ ions in acids, OH- ions in alkalis
If the question is about fuels:
Try to mention information about
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Combustion products – often CO2 and H2O
Pollution – from sulphur (burns to make SO2), soot (unburned hydrocarbons)
Eh = cmΔT experiment
CO2 impact on Global Warming (this is not pollution)
Examples from Specimen paper book:
Specimen Paper 1 Q 2 (d)
In 1825 bromine had been isolated from sea waterby Liebig who mistakenly thought it was a
compound of iodine and chlorine.
Using your knowledge of chemistry, comment on why he might have made the mistake.
Points to note:
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Cl, Br and I are in the same group of the periodic table and will have similar chemical
properties
They are all diatomic (Cl2, Br2 and I2)
They all have 7 outer electrons and a valency of 1
The formula of Iodine chloride would be ICl
The gfm of ICl is 162.5 and the GFM of Br2 is 160 – these values are very close
All molecules are covalent so would not conduct electricity when solid, molten of in solution
Could draw dot-cross bonding diagrams here for ICl and Br2
When Liebig tests the bromine he would find that it would have similar chemical and
physical properties to iodine chloride because Iodine, Bromine and Chlorine are all diatomic
(I2, Br2 and Cl2) and because iodine and chlorine have a valency of 1, iodine chloride would
have the formula ICl. They would have similar GFM’s (can show this), they are covalent
molecules, they would not conduct electricity when solid, molten or in solution and because
they are in the same column of the periodic table, they would have similar reactivity.
Specimen Paper 1 Q10
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Points to note:
Fertilisers are soluble salts containing the essential nutrients N, P or K
Two neutralisation reactions to form salts:
o Acid + alkali → salt + water
o Acid + carbonate → salt + water + carbon dioxide
o Write and balance the equation if you are confident
State that it requires neutralisation
There are various options you could pick to make the salt but the salt must have N, P or K in
it.
If you pick the potassium carbonate, you can tell the end point of the reaction as there will
be no more gas given off.
Need to talk about evaporating the water off at the end – could draw a diagram here.
The student should pick the acid and base that will give N, P or K in the product of the reaction. For
example, they could react:
Adding potassium carbonate and phosphoric acid will provide a neutral solution of the fertiliser
potassium phosphate containing the essential elements K and P. During the reaction, pH paper can
be used to test whether the solution is neutral – if the pH paper is dipped in and it turns green then
the sample can be evaporated to remove the water. CO2 gas will be formed and when it stops
forming this is also an indication that the acid is fully neutralised.
The equation for the reaction is : 3K2CO3 + 2H3PO4→ 2K3PO4 + 3H2O + 3CO2
Adding potassium hydroxide and nitric acid will provide a neutral solution of the fertiliser potassium
nitrate containing the essential elements K and N. During the reaction, pH paper can be used to test
whether the solution is neutral – if the pH paper is dipped in and it turns green then the sample can
be evaporated to remove the water.
The equation for the reaction is : KOH + HNO3→ KNO3 + H2O
I think it would be enough to select a pair of reactants, state why and comment that they have to be
neutralised, how you would do this, then describe the evaporation.
Correct pairs of reactants:
Acids
Bases
Salt formed
Nitric
ammonium hydroxide
ammonium nitrate
Phosphoric
ammonium hydroxide
ammonium phosphate
Phosphoric
potassium hydroxide
potassium phosphate
or potassium carbonate
Nitric
potassium hydroxide
or potassium carbonate
potassium nitrate